1. Field Of The Invention
The present invention relates to tools for bypassing fluid around a packer when a tool string is being run into, or removed from, a well bore, a more particularly, to a string bypass which is opened and closed responsive to pressure from a pump used to inflate the packer.
2. Description Of The Prior Art
When a tool string with a packer is lowered into a well bore, or removed therefrom, a problem arises because the packer, even when deflated or unactuated, is usually in relatively closer proximitity to the well bore than the other components of the tool string. As the tool string is moved longitudinally through the fluid in the well bore, the packer acts as a ram which does not allow a high flow rate of fluid therearound. This results in a much slower trip into or out of the well bore. To avoid this problem, bypass devices have been put in tool strings for allowing fluid to enter a portion of the tool string below the packer and exit a portion of the tool string above the packer. When the tool string is removed, the flow is reversed. Because fluid flows through this passageway rather than around the packer, there is less restriction as the tool string is moved through the well bore, and thus a much quicker trip is possible.
In many cases, it is undesirable to have such a bypass device open all of the time, and this is particularly true in testing tool strings which are used to test specific well formations. In such testing strings, normally a pair of inflatable packer are used with a flow port therebetween which is positioned adjacent the formation. The packers are inflated by a pump which is positioned in the testing string above packers and which pumps well annulus fluid or mud into the packers to place them in sealing engagement with the well bore. When running the testing string into the well bore, it is desirable to bypass fluid around the top packer through the flow port between the packers. However, this bypassing must be prevented when actually testing the fluids in the well formation. In other words, intercommunication between the formation to be tested and the well annulus above the top packer must be prevented during a testing operation. Thus, any string bypass for bypassing around the top packer must be closable prior to testing once the testing string is in position and the packers are inflated.
A mechanically actuated device which has been used as such a closable string bypass is the Halliburton "VR Safety Joint". The bypass is opened and closed by raising and lowering the tool string which results in relative longitudinal movement between an inner mandrel and an outer case in the safety joint. When the case and mandrel are relatively extended, the bypass is opened, and when the mandrel and case are moved relatively toward one another, the bypass is closed.
Problems result in usage of this manually actuated bypass, and one such situation may occur when the tool string encounters a tight spot in the well bore. This may result in the packers dragging on the tight spot with a resultant upward force on the packers causing the upper portion of the tool string to move relatively downward, thus shutting the bypass ports. When this occurs, bypassing is stopped, and the ram effect is once again a problem.
Another problem with the manually actuated bypass is that the testing string must be raised and lowered during the testing operation to actuate the tester valve and perhaps other components in the testing string. During testing, the bypass must be closed, and it is possible that during some of these raising and lowering operations, the bypass may be inadvertently opened which will dump well annulus hydrostatic pressure on the formation, ruining the test.
The string bypass of the present invention does not require any manual manipulation. Instead, a valve means is used which is closed in response to a differential pressure between the pump discharge and the well annulus. The bypass cannot be closed accidentally when running the testing string into the well bore. Also, the bypass cannot be inadvertently opened by manipulation of the tool string. The valve will only open to the bypassing position when the pressure between the pump discharge and the packers is relieved. In the system herein, this takes approximately 10,000 pounds pull at the surface which is considerably more than is required to manipulate the testing string during normal testing operations.